The present invention relates to a method of controlling a vehicle that is equipped with an engine, a clutch, and a gear-shift transmission, and it also relates to a vehicle equipped with a controlling apparatus or control device that works according to the method.
Many contemporary motor vehicles have transmissions with to several gear levels shifted manually by the driver of the vehicle. Likewise known is an automatic transmission that shifts in steps, but the latter type of transmission has the disadvantage of a higher cost in comparison to the manually shifted transmission.
The automatic transmission has the advantage of offering a higher level of comfort, but it also involves a higher level of technical complexity that puts the automatic transmission at a cost disadvantage. The cost factor is considered to be the main reason why only a small minority of cars of relatively low engine power are equipped with automatically shifting transmissions, or why some of the small cars are not even available with automatic transmissions. However, with the ever increasing volume of traffic, large and small cars alike are exposed to constantly changing traffic situations where the changes in speed require frequent gear shifts.
Some efforts are being undertaken to automate the operation of gear-shift transmissions in order to provide a higher level of driving comfort to users of motor vehicles that are not equipped with an automatic transmission. The approach in this development is based on the manual transmission, which will also be referred to as gear-shift transmission. A principal difference between an automated gear-shift transmission and an automatic transmission (with discrete speed levels) is that the latter can be shifted from one speed level to another without an interruption in the tractive force, while an automated gear-shift transmission requires the flow of torque from the engine through the clutch to the transmission to be interrupted during the gear-shifting process.
An automated gear-shift transmission allows gear levels to be changed automatically, but there is a time gap in traction during the shift process, in contrast to a multi-speed automatic transmission which can sustain a torque load during a shift. The gap in the tractive force becomes more noticeable to the driver, the higher the amount of traction that is being interrupted. After shifting gears, the engine has to build up traction again in order to accelerate the vehicle, so that the user of the motor vehicle will experience the gap in the tractive force as a change in the acceleration of the vehicle.
The present invention therefore aims in a broad and general sense to provide a method of controlling a vehicle that is equipped with a gear-shift transmission, so that the vehicle will shift gears with a high level of comfort. The invention also has the objective of providing a control device to perform the control function according to the inventive method.
The method proposed by the present invention as a solution to the problem stated above involves the following steps:
a) detecting when a gear-shift is about to be carried out in the transmission:
b) detecting the acceleration of the vehicle by means of a control device, and
c) reducing the acceleration of the vehicle to a first lower level of acceleration prior to the gear-shifting process.
The driver of a vehicle that is equipped with an automated gear-shift transmission can select an operating mode in which gears are shifted automatically. A control device can perform the shifting process by interrupting the flow of torque from the engine and by actuating the clutch and transmission according to the gear-shifting process that is to be performed. The driver of the motor vehicle will experience the gear-shifting process and the associated gap in vehicle traction as a fluctuation in the acceleration of the vehicle.
The invention therefore provides a method of controlling a vehicle equipped with a gear-shift transmission that is coupled to an engine by way of a clutch. According to the inventive concept, the acceleration of the vehicle is detected by a control device; and prior to initiating a gear-shifting process, the acceleration is lowered to a first acceleration level. The method according to the invention provides that prior to a gear change, the current acceleration of the vehicle is determined, e.g., based on a sensor signal by which the control device is informed of the engine torque or the acceleration, and that prior to a gear change, appropriate measures are taken to reduce the vehicle acceleration from the detected actual acceleration to a lower level of acceleration also referred to herein as the first acceleration level. According to the invention, the intent is to maintain the first acceleration level substantially unchanged for a prescribed time interval. Thus, the acceleration is lowered from the amount that was measured prior to initiating the gear shift and is then kept substantially constant at the lower level for a certain time interval.
Based on an analysis of the relevant human factors, the driver of a motor vehicle will take a relaxed body posture to the extent possible while driving the vehicle, in particular by attempting to carry his head in a balanced equilibrium position on the neck. If an unbalancing force is acting on the driver""s head, he will react by attempting to return his head to a position of equilibrium. In general, the processes that take place in this situation are not consciously experienced by the driver of a vehicle. When the head is in a balanced equilibrium position on the neck, the horizontal force components acting at the center of mass of the head will cancel each other, so that there is no resultant force that would tend to push the head out of its equilibrium. When a destabilizing resultant force occurs, e.g., due to a change in the dynamic situation of the vehicle, a person will react by attempting to return his head to the equilibrium position that existed before the onset of the destabilizing force.
The method according to the invention makes use of the foregoing observation. As a result of lowering the vehicle acceleration to the first acceleration level prior to performing a gear shift, the head of a driver or occupant of the vehicle is subjected to an inertial force and will as an immediate result be displaced in a forward direction out of its equilibrium position.
After the vehicle acceleration has been lowered to the first acceleration level, the latter level is kept substantially unchanged for a predetermined time interval. During this time interval, the driver will spontaneously (i.e., without being aware of the effort) attempt to restore his head to its equilibrium position. During this equilibrium-restoring phase, the acceleration of the vehicle remains substantially constant. Further according to the inventive method, before the driver has completed the process of restoring the equilibrium position of his head, the vehicle acceleration is lowered to a second acceleration level that is lower than the first level. The driver has no negative sensation of this further reduction in vehicle acceleration, because his sense of balance has already been primed to re-equilibrate his head in response to the first reduction of the acceleration.
According to the invention, the time interval during which the first acceleration level is kept substantially constant is longer than 100 to 200 milliseconds, the preferred interval being 200 to 600 milliseconds, which may be narrowed down to 300 to 500 milliseconds.
During this time interval, the driver will have returned his head about halfway towards the previous equilibrium position, i.e., by half the amount of the initial displacement. Thus, being in the middle of the re-equilibrating phase, the driver will experience no negative sensation from the additional reduction in vehicle acceleration.
According to the invention, a proposed magnitude for the first acceleration level is 40% to 70% of the vehicle acceleration as determined in the first step of the inventive method, which could be as high as the maximum possible acceleration of the vehicle.
According to a modified version of the inventive method, the time phase of the first acceleration level can include a short dip to near zero for a time interval of 50 to 100 milliseconds to unsettle the driver""s head from its equilibrium and thereby induce the aforementioned reaction of the driver to restore the previous state of equilibrium. Following the short dip in vehicle acceleration, the acceleration is raised back to the first level, so that the return movement of the driver""s head to its equilibrium position occurs mostly during the phase after the dip in the first level. While the return movement of the driver""s head is still in progress, the acceleration is cut back to the second acceleration level. With the modified method just described, the pronounced dip to near zero during the time phase of the first acceleration level serves to trigger a strong inertial response that causes the driver""s head to move forward. The pronounced dip in acceleration is followed by a short-term increase to the first acceleration level which, in accordance with the invention, is kept substantially constant for a prescribed time period, which helps the driver to return his head to the equilibrium position. About halfway in the return movement of the driver""s head, the acceleration is lowered to the second acceleration level. The second lowering of the acceleration will not cause any disagreeable sensation to the driver, because he has already tightened the muscles that hold and move the head. Thus, the vehicle acceleration overall varies according to a time pattern where the head of the driver is no longer jolted into an uncomfortable nodding movement.
According to the inventive method, the changes in vehicle acceleration are accomplished through a control of the engine torque. Prior to interrupting the traction in the process of shifting gears, the torque delivered by the engine is lowered to a first torque level that is lower than the amount of engine torque that corresponds to the acceleration that was determined in the first step of the inventive method. The control device maintains the engine torque at the aforementioned first level for a predetermined amount of time.
It is also possible to use a control pattern where during the predetermined time interval the amount of engine torque varies in a manner where the mean value of the torque during the time interval is lower than the amount of torque that would correspond to the previously measured acceleration. In an advantageous mode of variation, the engine torque is lowered over a time interval of about 200 to 800 milliseconds from an initial level to an ending level where the gear shift is started. During the time period of about 200 to 800 milliseconds, the engine torque is lowered from the level that corresponds to the previously measured acceleration to a first torque level. The decrease in acceleration causes the driver""s head to move from its equilibrium position which, in turn, triggers a response by the driver to return his head from a displaced position back to the equilibrium position. During the phase where the return to the equilibrium position is still in progress, the method according to the invention prescribes a further reduction of the engine torque to a second torque level that is lower than the first torque level. The driver will have no negative or uncomfortable sensation from the additional cutback in engine torque, because is occurs while the driver is in the process of returning his head from the displaced position to the equilibrium position. According to an advantageous embodiment of the invention, the two-step process of lowering the engine torque fills a time interval of about 200 to 800 milliseconds, which is followed by the gear-changing process.
To summarize the foregoing discussion, the invention provides a method suitable for implementation by means of a control device to control a vehicle with a gear-shift transmission that has to be in a torque-free state to shift gears. The vehicle has an engine coupled to the gear-shift transmission through a clutch. The method includes the steps of
a) detecting that a gear shift is called for,
b) determining the amount of engine torque that is present before initiating the shift,
c) lowering the engine torque from the level determined in step b) to a first torque level,
d) holding the engine torque at the first torque level for a predetermined time interval,
e) after the predetermined time interval, lowering the engine torque further, before
f) initiating the gear shift.
According to a further developed embodiment of the invention, the first torque level is maintained substantially unchanged for the length of time that the user of the vehicle needs to return his head about halfway after the nodding that was caused by the lowering of the torque to the first torque level. As explained above, the invention proposes to achieve the two-step reduction of the acceleration through a corresponding two-step reduction of the engine torque. In a vehicle equipped with an automated gear-shift transmission, the clutch that couples the transmission to the engine has to be disengaged before shifting gears. To prevent the engine from racing out of control after the clutch has been disengaged, the control device can be employed to take control over the engine torque, for example by controlling the throttle valve to change the amount of air supplied to the engine, or through an appropriate control of the ignition timing, or by controlling the rate at which fuel is supplied to the engine.
With the development efforts in the automobile industry to increase the efficiency of all components of the drive train in order to save fuel, one can observe a general trend to minimize the amount of damping in the individual components of the drive train. However, this makes the vehicle more prone to drive train oscillations which are irritating to the occupants of the vehicle and are therefore found to be detrimental to the riding comfort. Drive train oscillations manifest themselves as a back-and-forth jerking, shaking or jolting movement in the lengthwise direction of the vehicle. The invention therefore proposes a concept whereby the length of time spent at the reduced engine torque (i.e., at the first torque level) is to determined dependent on properties of the drive train of the vehicle. In this context, the length of time spent at the reduced engine torque is the amount of time between the first and the second cutback of the engine torque. The drive train of the vehicle first of all includes the engine itself, characterized in particular by its mass moment of inertia. In addition to the engine, the drive train includes all components of the vehicle that participate in transmitting power from the engine to the road surface such as, e.g., the clutch with its individual components, the transmission input shaft, the transmission with all of its components, the transmission output shaft, in some cases a drive shaft with universal joints, the axle gear assembly, the driving shafts and the driven wheels. Collectively, all drive train components downstream of the transmission, i.e., on the output side of the transmission, can be characterized by their combined elasticity, which will be referred to as the output-side elasticity.
The invention proposes a concept whereby the length of time spent at the reduced engine torque is determined dependent on the oscillation behavior of the drive train of the vehicle.
According to a further developed embodiment of the invention, the length of time spent at the reduced engine torque is set dependent on the period of the drive train oscillations of the vehicle, i.e., the oscillation period of the aforementioned back-and-forth jolting movement. The period of the drive train oscillations is a characteristic parameter specific to each gear level. The shortest oscillation period occurs in the highest gear level, and the longest period occurs in the lowest gear level. This is best understood by considering the drive train as a spring oscillator in which the aforementioned output-side elasticity is equated to a spring and the mass moment of inertia of the engine is equated to the inertial mass of the spring oscillator. With the spring and the inertial mass in this case being coupled through one of the different gear levels of the transmission, the resulting spring oscillator is stiffest in the highest gear because the engine performs the smallest number of rotations for each rotation at the output side of the transmission. The period of the drive train oscillation is to a large extent determined by the mass moment of inertia of the engine and by the output-side elasticity.
The invention therefore provides the concept that the length of time spent at the reduced engine torque is set dependent on the period of the drive train oscillation. It is further advantageous to also consider the current engine torque (as measured or detected) in the determination of the length of time spent at the reduced engine torque. In a further developed embodiment of the invention, the interval at the reduced engine torque is determined dependent on the detected current engine torque and on a length of time corresponding substantially to one-half of the gear-specific period of drive train oscillation.
To execute the method just described, the control device (having determined that a gear shift needs to be carried out) sends a signal to the engine to effect a first cutback of the engine torque dependent on the detected current engine torque level and also dependent on the approximate length of a half-period of the drive train oscillation. The signal that the control device sends to the engine is a control target for the engine torque. Due to factors inherent in the system, the engine follows the target command with a certain time lag. It is therefore advantageous to allow a predetermined amount of waiting time elapse after sending the target signal, to allow the actual engine torque to fall to, e.g., 80% of the initially detected torque level. This is followed by a further waiting interval corresponding to the gear-specific amount of time for a half-period of the drive train oscillation, whereupon the control device issues a signal for a further cutback of the engine torque, i.e., another control target for the engine torque. The time from the signal for the first cutback to the signal for the second cutback of the engine torque is thus determined based on the gear-specific time interval for a half-period of the drive train oscillation and another time interval as required to allow the engine torque to fall by about 20%.
Also as a part of the method, the invention provides that the control device issues a signal to a clutch actuator device (where the clutch is, e.g., a friction clutch) to adjust the clutch torque (i.e., the torque-transmitting capacity of the clutch) so that it follows the cutbacks of the engine torque. By adapting the clutch torque to the actually delivered engine torque at each point in time, it is possible to reduce the time required for the subsequent complete disengagement of the clutch.
The invention provides that the control device signals the clutch actuator device to disengage the clutch at a point in time when the drive train elements downstream of the gear-shift transmission, i.e., the elements that contribute to the output-side elasticity, are substantially in an unbiased, tension-free state. It is advantageous to allow some lead time in the actuator signal to compensate for the processing time of the control device and the inertia of the actuator. If the time of clutch disengagement were not controlled, the aforementioned drive train elements could be elastically biased by the torque that is transmitted through them. The release of the elastic tension at the disengagement of the clutch would cause a change in the rpm rate of the clutch disc, which would lead to an oscillation. Thus, an elastic bias torque or state of tension caused by the output-side elasticity in the drive train may be experienced by the occupants of the vehicle as an uncomfortable jolt during the disengagement of the clutch.
The invention also provides that the control device sends a signal to an actuator device of the automated gear-shift transmission to shift out of gear at a point in time when the drive train elements downstream of the gear-shift transmission, i.e., the elements that contribute to the output-side elasticity, are substantially in an unbiased, tension-free state. It is advantageous to allow some lead time in the actuator signal to compensate for the processing time of the control device and the inertia of the actuator. If the time of shifting out of gear were not controlled and if the aforementioned drive train elements were elastically biased, the out-shifting, i.e., the disengagement of a sliding sleeve of the transmission from a spline, would require a large amount of force. The release of the elastic tension at the disengagement of the tooth profiles causes a change in the rpm rate of internal components of the transmission, which could even involve the risk of damaging the affected components.
As stated previously, the invention provides a method suitable for implementation by means of a control device to control a vehicle with a gear-shift transmission, an engine and a clutch. The method has the steps of
a) detecting that a gear shift is to be performed,
b) determining the amount of engine torque that is present before initiating the shift,
c) lowering the engine torque from the level determined in step b) to a first torque level,
d) holding the engine torque at the first torque level for a predetermined time interval,
e) after the predetermined time interval, lowering the engine torque further, before
f) initiating the gear shift.
As discussed above, before initiating the gear shift in the foregoing step f), the clutch is taken out of engagement. In the process of disengaging and re-engaging, the clutch goes through slip phases. The slipping clutch causes oscillations in the drive train, which will herein be referred to as chatter vibrations. Chatter vibrations occur in cases where oscillatory torque fluctuations induced by the slippage of the clutch coincide with resonance frequencies of the drive train as the latter is dynamically interrupted by the clutch. It has been found that in case of an elastic bias torque in the output-side elements of the drive train, the resulting rpm change at the disengagement of the clutch is experienced as an uncomfortable jolt only if the release of the elastic bias torque causes an oscillation that extends over more than one-fourth of an oscillation period, i.e., if the clutch disengagement takes longer than one-fourth of a chatter-vibration period. It has also been found that a loss of riding comfort is experienced if the time interval for the cutback of the engine torque is shorter than the period of the drive train oscillation, but that the drive train oscillation itself causes an adverse sensation only if it lasts longer than one-fourth of a period of the drive train oscillation.
The invention therefore provides that the control device sends a signal to the engine to lower the engine torque in such a manner that the length of time spent at the reduced engine torque corresponds substantially to one-fourth of the period of the oscillation period for the currently engaged gear level or, alternatively, in a manner where the time period for lowering the engine torque is either longer than the period of the drive train oscillation or shorter than one-fourth of the period of the drive train oscillation, while at the same time the interval for disengaging the clutch corresponds substantially to one-fourth of a period of the chatter vibration.
The invention also includes a control device that performs the method of the foregoing description which is used to control a vehicle equipped with a gear-shift transmission that is coupled to an engine by way of a clutch. The control device is equipped to detect when a gear shift is needed in the transmission, to also detect the current acceleration of the vehicle, and to perform the functions involved in lowering the acceleration to a first acceleration level prior to the gear-shifting process. According to an advantageous embodiment of the invention, the control devices keeps the first acceleration level substantially constant during a predetermined time period.
According to another embodiment, the control device is designed to produce a first acceleration level that varies over the predetermined time period in a manner where the mean value of the reduced acceleration during the predetermined time period is smaller than the initially detected acceleration of the vehicle. The control device is further designed so that it can lower the vehicle acceleration to a second acceleration level that is lower than the first acceleration level.
The control device can change the acceleration of the vehicle by controlling the torque delivered by the engine. In specific terms, this means that the control device is designed to control the ignition timing of the engine to effect a change in vehicle acceleration. As another possibility, the control device can control the fuel supply to the engine as a way of managing the engine torque. In addition or as an alternative, the control device could also be equipped to control the air intake of the engine in order to influence the acceleration of the vehicle.
To control the amount of torque delivered by the engine, the control device is equipped to send a signal to the engine to lower the torque in such a manner that the length of time spent at a reduced engine torque prior to disengaging the clutch corresponds to substantially one-fourth of a period of the drive train oscillation which, as discussed above, depends on the gear that is currently set in the transmission. As alternative possibilities, the length of time spent at a reduced engine torque prior to disengaging the clutch may be longer than a full period of drive train oscillation or shorter than one-fourth of a period of drive train oscillation, while the time interval for taking the clutch out of engagement substantially corresponds to one-fourth of a period of the chatter vibration.
The invention also covers a vehicle with a gear-shifting transmission that is preferably automated and is coupled to the engine of the motor vehicle through a friction clutch. The vehicle has a control device as described above. A driver of the motor vehicle can select an operating mode of the control device where the latter controls a clutch actuator device and a transmission actuator device, so that the gear changes are performed automatically and the riding comfort is not negatively affected by drive train oscillations of the vehicle.
In a known type of vehicle with a manual shift transmission, the driver and passengers are alerted about an impending gear shift at the time when the driver closes his grip on the shift lever to perform a manual gear change. Having been alerted, the occupants will no longer find the gap in vehicle traction to be noticeably uncomfortable when the clutch is disengaged.
According to an advantageous embodiment of the invention, the vehicle is equipped with an indicator device that alerts the user of the vehicle when a gear shift is imminent. The indicator device can be an acoustical and/or optical and/or haptic (tactile) display. The indicator device alerts the user of the vehicle with the automated gear-shift transmission when a gear shift is imminent, so that he will not be surprised by the subsequent interruption in the traction of the vehicle. The indicator device can be modified so that it will also indicate the targeted new gear level that the transmission will subsequently be shifted to. This is advantageous in certain applications, e.g., when an intermediate gear level is to be skipped in an up-shift.
The novel features that are considered as characteristic of the invention are set forth in particular in the appended claims. The improved apparatus itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain presently preferred specific embodiments with reference to the accompanying drawing.